While singers are dependent on the physics of sound, it is a less definable ingredient that transcends the sterile grasp of science that most vocalists concern themselves with. It is the ingredient that stirs a yearning in the heart, or causes a smile of understanding. It can move you to tears or dope you into dancing like a fool. It is the ingredient that lurks deep, deep down in the secret chambers of the heart. A good singer will find that place within us and bring it out, from one soul to...